In The Godfather, Luca Brasi is one of Don Vito Corleone's personal enforcers. Brasi is portrayed as slow-witted and brutish, but his ruthlessness and his fierce loyalty to Don Corleone means he is both feared and respected. Fluent in Italian and able to handle himself in any fight, he has a dark reputation among the underworld as a savage killer. Vito Corleone describes Luca Brasi (and later Al Neri) as a "man who goes around life with a sign that says 'kill me' painted on, this makes everyone want to kill him, but yet no one can. Eventually this man finds someone who doesn't want to kill him and fears that his man is the only one who can kill him".
At his sister's wedding, Michael Corleone tells his then girlfriend Kay Adams the story of how Don Corleone helped his godson Johnny Fontane. Michael explains that his father went to convince Les Halley, the bandleader, to release Johnny from a personal service contract that was holding back Johnny's singing career. Halley refused both the inital offer of $20,000 and the following offer of $10,000, completely missing the significance of that lower offer. Don Corleone returned the next day with Genco Abbandando, his consigliere, and Luca Brasi. Within an hour the bandleader signed a release for only $10,000 (in the film, the figure was changed to $1000). Luca Brasi had held a gun to the bandleader's head while Don Corleone assured him that either his brains or his signature would be on the release contract. In the movie, that was called "an offer he couldn't refuse", though in the novel this euphemism was applied by Don Corleone to the yet to be made offer to Jack Woltz, another man who had been holding back Johnny's career.
Shortly before Vito Corleone is shot, Brasi (on Vito Corleone's instructions) intends to draw out rival mobster Virgil Sollozzo and the rest of the Don's enemies. Brasi then meets with Bruno Tattaglia, the son of one of the Don's rival bosses, Philip Tattaglia. Sollozzo shows up, and after promises of friendship and a job offer, rams a knife into Luca's hand, pinning it to the bar. An assassin then garrottes him from behind. They then throw Brasi's lifeless body into the sea.
A Sicilian message is later sent to the Corleone family: a fish wrapped in Brasi's bulletproof vest. The meaning is made clear to the Corleones: Brasi is now at the bottom of the ocean (or as Corleone caporegime Sal Tessio explains, "It's an old Sicilian message. It means Luca Brasi sleeps with the fishes"). Sollozzo has Brasi killed as it is the best way of ensuring Vito Corleone's vulnerability. When Tom Hagen is kidnapped by Sollozzo, Hagen warns of reprisals from Luca Brasi about Vito Corleone (not knowing Luca had been killed), saying that while he'll try to persuade Sonny to let the family go into narcotics, "even Sonny won't be able to call off Luca Brasi."
It is mentioned in the novel and implied in the film that Brasi is perhaps the only man Vito Corleone fears and vice versa. It is also implied that Brasi was created to portray real life Gambino Mafia Hitman Santo "Sonny Boy" Ricchiettore although truth to that is not certain.
Brasi's talent, it was said, was that he could do a job, or murder all by himself, without confederates, which made a criminal conviction almost impossible. He is also known for killing, in two weeks, six men who attempted to kill Don Corleone. These six deaths ended the famous "Olive Oil War".
In the novel, Michael learns that, years earlier, Brasi had impregnated a young Irish prostitute and later murdered her. Brasi did not stop there; On the day of his daughter's birth, he forced the midwife, under pain of death, to hurl the child into a furnace, an act for which she never forgave herself. The midwife describes him as an unholy demon.
Another early incident involved Brasi killing off two of Al Capone's henchmen hired to kill Don Corleone. Brasi subdued both of them and tied and gagged them with towels stuffed in their mouths. He then hacked one of them to pieces with an axe. When he went to finish off the other one, he found that the man had gone through a shock convulsion and choked to death on the towel.
Brasi's role as personal enforcer/bodyguard to the Don is later filled by Al Neri.